DATA STRUCTURE DETERMINING METHOD FOR HIERARCHICALLY STRUCTURED DATA CORRESPONDING TO IDENTIFIERS AND APPARATUS THEREOF

A structure of hierarchically structured data including two or more data pieces having a hierarchical relationship is determined. An identifier is added to a data piece that is an element of the hierarchically structured data. The method determines whether or not there are two or more data pieces with the same identifier as the identifier of a first data piece, in a hierarchical data sequence composed of the first data piece and a second data piece placed below the first data piece, determines that an infinite hierarchical structure takes place when there are two or more data pieces with the same identifier if the second data piece is placed below the first data piece, and determines that an infinite hierarchical structure does not take place when there are not two or more data pieces with the same identifier, even if the second data piece is placed below the first data piece. Corresponding to the determined result, the data placement that results in an occurrence of an infinite hierarchical structure can be prevented.